Mold for preparing large-size rare earth magnesium alloy ingot without tail shrinkage by back pressure severe plastic deformation

ABSTRACT

The present disclosure discloses a mold for preparing large-size rare earth magnesium alloy ingot without tail shrinkage by back pressure severe plastic deformation, which includes a male mold, a female mold, a recoverable discard block and a back pressure plate connected with a pushing cylinder of the press machine. The female mold is provided with an upper mold cavity and a lower mold cavity, an upper part of the upper mold cavity is configured for placing blanks, the recoverable discard block and the male mold, and a lower part of the upper mold cavity is inclined inward to form an extrusion deformation area. The recoverable discard block is configured to be filled in an extrusion deformation area and restored through deformation. The present disclosure can solve the existence of the discard in the traditional forward extrusion and the tail shrinking phenomenon caused by the uneven metal flow.

FIELD OF THE INVENTION

The present disclosure relates to the technical field of metal plasticprocessing, in particular to a mold for preparing large-size rare earthmagnesium alloy ingot without tail shrinkage by back pressure severeplastic deformation.

BACKGROUND OF THE INVENTION

As shown in FIG. 1 , in metal plastic deformation molds, traditionalforward extrusion is the most basic extrusion method. Because of itshigh triaxial compressive stress, traditional forward extrusion canfully improve the plastic deformation ability of metal materials, whichhas the characteristics of simple process operation and great productionflexibility, and is widely used. However, the following disadvantagesstill exist: (1) during extrusion, the metal flow is uneven, the metalflow is fast in the middle and is slow in the edge, as shown in positionA in FIG. 2 , resulting in tail shrinkage, which is not conducive tocontinuous extrusion. (2) There is a conical deformation zone in theextrusion mold, so that there is still discard after extrusion. Theexistence of discard and tail shrinkage makes it necessary to cut thehead and tail after extrusion, resulting in material waste. (3) Theexisting large-size magnesium alloys are usually prepared by the processof “multiple heating, repeated extrusion and upsetting”, that is, 1)heating homogenization—2) heating—3) extrusion—4) head and tailremoval—5) heating—6) upsetting, and repeating the steps 2)—6) threetimes, a total of 16 processes, with a large cumulative total strain of3-4, which has a certain strengthening and toughening effect. However,the gap of each upsetting and extrusion cycle in this process needs tobe reheated. In addition to high energy consumption, each heating willweaken the strengthening effect and greatly reduce the strengtheningeffect. In addition, the gap of each upsetting and extrusion cyclerequires the cutting of the discard, which has long working hours, lowmaterial utilization and low production efficiency, resulting in highcomprehensive cost and limiting the application of mass production ofmagnesium alloys.

SUMMARY OF THE INVENTION

The object of the present disclosure is to provide a mold for preparinglarge-size rare earth magnesium alloy ingot without tail shrinkage byback pressure severe plastic deformation, so that the blank in theextrusion process under the condition of back pressure is continuouslyupsetting, to achieve the preparation of large-size blank. And reusablerecoverable discard blocks are used in the late extrusion, so as tosolve the existence of discard in the traditional forward extrusion andthe shrinkage tail phenomenon caused by the uneven flow of metal, whichwill save materials and shorten the process, so that the strengtheningeffect is increased, and the production time is greatly reduced.

In order to achieve the above object, the solution of the presentdisclosure is a mold for preparing large-size rare earth magnesium alloyingot without tail shrinkage by back pressure severe plasticdeformation, which includes a male mold installed on an upper workbenchof a press machine, a female mold installed on a lower workbench of thepress machine, a recoverable discard block and a back pressure plateconnected with a pushing cylinder of the press machine. The female moldis provided with an upper mold cavity and a lower mold cavity, an upperpart of the upper mold cavity is configured for placing blanks, therecoverable discard block and the male mold, and a lower part of theupper mold cavity is inclined inward to form an extrusion deformationarea communicated with the lower mold cavity.

The recoverable discard block is separated between the blank and themale mold, the recoverable discard block is made of deformable material,and the recoverable discard block can not only be deformed and filled inan extrusion deformation area, but also be deformed and restored.

The upper part of the back pressure plate is fitted in the lower moldcavity, so that a molding cavity is formed between the upper part of theback pressure plate and the lower mold cavity, and the upper surface ofthe back pressure plate is raised in the middle.

Further, the recoverable discard block is in a molten state at hightemperature, and the recoverable discard block is a brittle solid at lowtemperature and is broken into solid powder when pressed in theextrusion deformation area.

Further, the present disclosure further includes an extrusionrestoration mold, wherein the recoverable discard block is crushed intosolid powder under pressure and then put into the extrusion restorationmold to restore into the recoverable discard block.

Further, the extrusion restoration mold includes a pressing box and apressing block, the pressing box is provided with a groove, therecoverable discard block is crushed into solid powder under pressureand placed in the groove, and the pressing block presses the solidpowder to restore the solid powder into recoverable discard block underhigh temperature.

Further, the recoverable residue block is made of a mixture of fluoritepowder and graphite.

Further, the upper part of the lower mold cavity is inclined to expandoutward from top to bottom, so that the side part of the extrusiondeformation area forms an annular inner flange.

Further, the width of the lower mold cavity is greater than that of theupper mold cavity.

Further, the back pressure plate is in T-shape.

After adopting the above solution, the advantageous effect of thepresent disclosure lies in:

In the extrusion process of the present disclosure, because therecoverable blank can gradually fill the extrusion deformation area withthe movement of the mold, so that the cylinder blank can be completelyextruded into the lower mold cavity, there is no blank problem in thefinal formed part. In addition, in the upsetting extrusion process, thesurface raised structure on the back pressure plate provides backpressure to make the deformation uniform, and at the same time, it canprevent the blank from tail shrinking, so that the formed part does notneed to cut the head and tail again, which saves materials. The reuse ofthe recoverable discard block is simple and environmentally friendly.Besides, the strain of the present disclosure increases in the wholeprocess, which is conducive to increasing the strengthening effect, andprovides a basis for the preparation of the severe deformation ofmagnesium alloy ingots. Further, it not only reduces the number ofupsetting extrusion, but also reduces the cutting process, so as toimprove the overall production efficiency and expands the application ofmass production of magnesium alloy without tail shrinkage, back pressureand severe plastic deformation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more readily apparent to thoseordinarily skilled in the art after reviewing the following detaileddescription and accompanying drawings, in which:

FIG. 1 is a structural diagram of the existing forward extrusion metalplastic deformation mold before forming;

FIG. 2 is a structural diagram of the existing forward extrusion metalplastic deformation mold after forming (there are blank residual afterpressing and tail shrinkage phenomena);

FIG. 3 is a structural diagram of the mold of the present disclosurebefore forming;

FIG. 4 is a structural diagram when the bottom of the blank of the moldof the present disclosure is in contact with the back pressure plate;

FIG. 5 is a structural diagram of the upsetting extrusion process of themold of the present disclosure;

FIG. 6 is a structural diagram of the forming end of the mold of thepresent disclosure;

FIG. 7 is an enlarged schematic diagram shown that the fragmentation ofthe recoverable discard block after the upsetting extrusion process ofthe present disclosure;

FIG. 8 is a schematic diagram of the structure for taking out therecoverable residue powder of the present disclosure;

FIG. 9 is a schematic diagram of the structure shown that the powderedrecoverable discard block of the present disclosure is placed into theextrusion restoration mold;

FIG. 10 is a schematic diagram of the structure shown that therecoverable discard block of the present disclosure is restored; and

FIG. 11 is a schematic diagram of arc balance friction on the uppersurface of the back pressure plate of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In order to more clearly illustrate the embodiments of the presentdisclosure or the technical solutions in the prior art, the followingwill briefly introduce the drawings that need to be used in thedescription of the embodiments or the prior art. It is apparent that thedrawings in the following description are only some embodiments of thepresent disclosure. For those skilled in the art, other drawings can beobtained from these drawings without paying creative labor.

The present disclosure is a mold for preparing large-size rare earthmagnesium alloy ingot without tail shrinkage by back pressure severeplastic deformation, as shown in FIG. 3 , which includes a male mold 1installed on an upper workbench (not shown) of a press machine, a femalemold 2 installed on a lower workbench (not shown) of the press machine,a recoverable discard block 3, a back pressure plate 4 and connectedwith a pushing cylinder (not shown) of the press machine, and anextrusion restoration mold 6 (shown in FIGS. 9 and 10 ).

The female mold 2 is provided with an upper mold cavity 21 and a lowermold cavity 22. The upper mold cavity 21 and the lower mold cavity 22are located on the same central axis, and the upper part of the uppermold cavity 21 is configured for placing blanks 5, the recoverablediscard block 3 and the male mold 1. There is an extrusion deformationarea 23 provided between the upper mold cavity 21 and the lower moldcavity 22. The lower part of the upper mold cavity 21 is inclined inwardto form the extrusion deformation area 23 communicated with the lowermold cavity 22. The upper part of the lower mold cavity 22 is connectedwith the extrusion deformation area 23. The upper part of the lower moldcavity 22 is inclined to expand outward from top to bottom, so that theside part of the extrusion deformation area 23 forms an annular innerflange 24, and the formed multiple turning angles improve the plasticdeformation degree. The back pressure plate 4 is T-shaped, and the upperpart of the back pressure plate 4 is fitted in the lower mold cavity 22to form a molding cavity between the upper part of the back pressureplate 4 and the lower mold cavity 22, and the lower part of the backpressure plate 4 is connected to the pushing cylinder of the pressmachine.

As shown in FIG. 4 , the width of the blank 5 extruded by the extrusiondeformation area 23 is d, and the width D of the lower mold cavity 22 ismuch larger than the width dl of the upper mold cavity 21, so thatsevere plastic deformation ε can be realized:

${\varepsilon = {{\varepsilon_{1}\left( {2Ln\frac{d}{d_{1}}} \right)} + {\varepsilon_{2}\left( {2Ln\frac{D}{d}} \right)}}};$

wherein, ε₁ is the strain at which the blank diameter changes from d1 tod, ε₂ is the strain at which the blank diameter changes from d to D.

Further, to achieve severe plastic deformation ε₂, it is necessary todesign the upper surface of the back pressure plate 4 as an externalconvex structure, that is, the middle of the upper surface of the backpressure plate 4 is raised. In order to prevent tail shrinkage andcounteract the friction that prevents metal flow during upsetting, thusthe following formula is satisfied:

${{\frac{d}{4h} \cdot \frac{\cos\theta}{1 + {\frac{d\mu}{2h}\left( {1 - {\sin^{2}\theta}} \right)}}} \leq 1};$

As shown in FIG. 11 , it is the stress decomposition state when thedistance between the upsetting metal and the central axis is L. Thecontact surface of the upsetting metal with the back pressure plate 4generates a frictional force that prevents the flow of the metal whenthe upsetting metal flows outward, and the back pressure plate isdesigned as a raised surface with a certain angle θ instead of a flatsurface. The stress given by the outside can be decomposed into thestress 94 _(Z) in the normal direction of the contact surface andtangential stress σ_(tan), and the tangential stress σ_(tan) counteractsthe friction. In addition, h is the height of upsetting extrusion blank,d is the diameter of upsetting extrusion blank, and μ is the frictioncoefficient. The height of the back pressure plate is greater than theheight of the lower mold cavity of the female mold, and the mold canrealize the preparation of large-size magnesium alloy ingots (diameterD>400, total strain ε>4).

As shown in FIG. 3 , the recoverable discard block 3 is separatedbetween the blank 5 and the male mold 1. The recoverable discard block 3is made of deformable materials, which can be made of a mixture mixedwith fluorite powder and graphite as the main raw materials. Therecoverable discard block 3 is in a molten state at high temperature andis a brittle solid state at low temperature, and the recoverable discardblock 3 is broken into solid powder when pressed in the extrusiondeformation area 23 at low temperature. As shown in FIG. 6 , therecoverable discard block 3 can be filled in the extrusion deformationarea 23 and restored through deformation. As shown in FIG. 9 and FIG. 10, about the restored way, an extrusion restoration mold 6 is providedfor the restoring, the extrusion restoration mold 6 includes a pressingbox 61 and a pressing block 62, the pressing box 61 is provided with agroove, the recoverable discard block 3 is crushed into solid powderunder pressure and placed in the groove, and the pressing block 62presses the solid powder under high temperature, so that the solidpowder is compressed and deformed back recoverable discard block.

The present disclosure further provides a method for preparinglarge-size rare earth magnesium alloy ingot without tail shrinkage byback pressure severe plastic deformation, and the method includes thefollowing steps:

-   -   S1: providing cylindrical magnesium alloy bar;    -   S2: homogenizing the cylindrical magnesium alloy bar as cylinder        blank 5;    -   S3: heating the cylinder blank 5 to the forming temperature and        holding the temperature, and heating the preparation mold, back        pressure plate 4, pressing box 61 and pressing block 62 above        the experimental temperature and holding the temperature for        half an hour;    -   S4: installing the preparation mold after preheating and heat        preservation on the pressing machine, and evenly spraying        organic graphite lubricant on the male mold 1 and the female        mold 2;    -   S6: putting the cylinder blank 5 after homogenization and heat        treatment into the upper mold cavity 21 of the male mold 2;    -   S7: placing the recoverable discard block 3 above the cylinder        blank 5;    -   S8: in the initial stage of extrusion forming, adjusting the        height of the back pressure plate 4 to the outlet of the        extrusion deformation area 23 by the upward movement of the        pushing cylinder. First, the pressing machine drives the male        mold 1 to move downward and gradually extrudes the cylinder        blank 5 into the extrusion deformation area 23. As shown in FIG.        4 , the bottom of the cylinder blank 5 slowly deforms, contracts        and fills the extrusion deformation area 23. As the male mold 1        continues to move downward, the bottom of the blank 5 contacts        the upper surface of the back pressure plate 4. When the contact        width is close to the size of the extruded part, as shown in        FIG. 5 , the back pressure plate 4 starts its downward return        with the male mold 1. After the stroke of the male mold 1 is        completed, as shown in FIG. 6 , the recoverable discard block 3        fills the extrusion deformation area 23, and the upsetting        deformation is completed. In this process, the back pressure        plate 4 always gives an upward back pressure to blank 5;    -   S9: then, driving the back pressure plate 4 downward to remove        from the lower part of the lower mold cavity 22 by the pushing        cylinder, and the recoverable discard block 3 has been broken        due to high pressure; then taking out the extruded cylinder        blank 5 and the powder of the recoverable discard block 3 from        the lower part of the lower mold cavity 22, putting the broken        powder of recoverable discard block 3 into the heated pressing        box 61, and pressing down with the pressing block 62 to restore        the powder of the recoverable discard block 3 into a plate        shape, so that the recoverable discard block 3 can be used next        time.

The male mold 1 and the female mold 2 are connected to the upper andlower workbenches through fasteners. The method also includes S10: afterthe work is completed, molding the male mold 1 and the mold 2 togetherto perform a mold closing action, then loosening the fasteners, and thenremoving the preparation mold.

The description above is only a preferred embodiment of the presentdisclosure, not a limitation on the present application. All equivalentmodification made based on the principle of the present applicationshall fall into the scope of the present application.

What is claimed is:
 1. A mold for preparing large-size rare earthmagnesium alloy ingot without tail shrinkage by back pressure severeplastic deformation, comprising a male mold installed on an upperworkbench of a press machine, a female mold installed on a lowerworkbench of the press machine, a recoverable discard block and a backpressure plate connected with a pushing cylinder of the press machine,wherein the female mold is provided with an upper mold cavity and alower mold cavity, an upper part of the upper mold cavity is configuredfor placing blanks, the recoverable discard block and the male mold, anda lower part of the upper mold cavity is inclined inward to form anextrusion deformation area communicated with the lower mold cavity; therecoverable discard block is separated between the blank and the malemold, the recoverable discard block is made of deformable material, andthe recoverable discard block is configured to be deformed and filled inan extrusion deformation area and restored through deformation; an upperpart of the back pressure plate is fitted in the lower mold cavity, amolding cavity is formed between the upper part of the back pressureplate and the lower mold cavity, and an upper surface of the backpressure plate is raised in a middle.
 2. The mold for preparinglarge-size rare earth magnesium alloy ingot without tail shrinkage byback pressure severe plastic deformation according to claim 1, whereinthe recoverable discard block is in a molten state at high temperature,and the recoverable discard block is a brittle solid at low temperatureand is broken into solid powder when pressed in the extrusiondeformation area.
 3. The mold for preparing large-size rare earthmagnesium alloy ingot without tail shrinkage by back pressure severeplastic deformation according to claim 2, wherein the mold furthercomprises an extrusion restoration mold, wherein the recoverable discardblock is crushed into solid powder under pressure and then put into theextrusion restoration mold to recover into the recoverable discardblock.
 4. The mold for preparing large-size rare earth magnesium alloyingot without tail shrinkage by back pressure severe plastic deformationaccording to claim 3, wherein the extrusion restoration mold comprises apressing box and a pressing block, the pressing box is provided with agroove, the recoverable discard block is crushed into solid powder underpressure and placed in the groove, and the solid powder is restored intorecoverable discard block under high temperature.
 5. The mold forpreparing large-size rare earth magnesium alloy ingot without tailshrinkage by back pressure severe plastic deformation according to claim1, wherein the recoverable residue block is made of a mixture offluorite powder and graphite.
 6. The mold for preparing large-size rareearth magnesium alloy ingot without tail shrinkage by back pressuresevere plastic deformation according to claim 1, wherein an upper partof the lower mold cavity is inclined to expand outward from top tobottom, so that a side part of the extrusion deformation area forms anannular inner flange.
 7. The mold for preparing large-size rare earthmagnesium alloy ingot without tail shrinkage by back pressure severeplastic deformation according to claim 1, wherein a width of the lowermold cavity is greater than that of the upper mold cavity.
 8. The moldfor preparing large-size rare earth magnesium alloy ingot without tailshrinkage by back pressure severe plastic deformation according to claim1, wherein the back pressure plate is in T-shape.